The present invention is directed to a method for separating harmful substances, such as SO.sub.2, HCl and NO.sub.x where x is 1 or 2, for example, from combustion exhaust gases, by way of dry adsorbents based upon hydrated oxides, hydroxides, or oxides. Such dry adsorbents include Ca(OH).sub.2, AlOOH, Al(OH).sub.3, Al.sub.2 O.sub.3 xH.sub.2 O, bauxite, CaO, NaOH, and/or carbonates, and/or hydrogen carbonates. The exhaust gases so treated, have high combustion chamber temperatures, such as attained by bituminous coal firing, for example.
In the present invention, the powdered or particulate adsorbents, are blown into at least a portion of the flowing exhaust gas at an exhaust gas temperature below about 400.degree. C., thereby binding any chlorides which may be present in the exhaust gas. The exhaust gases or fumes are subsequently released into the open environment through a chimney, after precipitation of the solid components therefrom. The present invention also relates to an apparatus for carrying out this procedure.
DE-OS No. 31 39 080 discloses the blowing or injection of Ca(OH).sub.2 adsorbent into a waste or refuse boiler at a flue gas temperature of 400.degree. to 350.degree. C. in order to separate the chlorine and/or fluorine from the flue gases of a waste or refuse incinerator, and to bind these harmful substances. The exhaust gases are then cleaned and transmitted into the atmosphere. The disadvantage of this procedure and apparatus, is that the exhaust gases containing the dust and adsorbents, are directed through the final heating surfaces, so that the gases quickly pollute the environment. The combined separation of dust and chlorides or fluorides leads to an intimate mixture of these three components, thus making separation and further treatment practically impossible. Simultaneous adsorption of SO.sub.2 and/or reduction of NO.sub.x or sulphate formation, is not indicated.
It is known that adsorption is more efficient in a "wet" manner than in a "dry" condition for the separation of SO.sub.2 -containing harmful fumes from the exhaust gases. It is also known that in the case of the "dry" separation of the harmful fumes, at similar surface boundary conditions, but with different exhaust gases, the degree of separation is subject to large fluctuations, whereby refuse firing generally produces a better degree of separation than coal firing.